To express an activity began in the past and is still going on.For definite time we use ‘Since’ & for duration of time we use ‘For’
She has been dancing for an hour.
Subject + has/have + been + v3rd form + ing + object
I have been studying since 2 o’clock
Subject + has/have + not + been + v3rd form + ing + object
She has not been singing for two hours.
has/have +Subject + been + v3rd form + ing + object
Have you been waiting for an hour?